Polyol ester lubricants for hermetically sealed refrigerating compressors

ABSTRACT

A high quality lubricant for hermetically sealed domestic air conditioner and refrigerator compressors, especially those using chlorine free hydrofluorocarbon refrigerant working fluids, is provided by mixed esters of hindered polyols, most desirably pentaerythritol, with a mixture of carboxylic acids including at least some iso-pentanoic acid along with either or both of iso-nonanoic acid and dibasic acids such as adipic.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.09/346,872 now abandoned, filed Jul. 2, 1999, which is a continuation ofU.S. patent application Ser. No. 08/537,167, filed Sep. 29, 1995, nowU.S. Pat. No. 6,221,272, issued Apr. 24, 2001, which is a continuationof U.S. patent application Ser. No. 08/268,879, filed Jun. 30, 1994, nowabandoned, which is a continuation of U.S. patent application Ser. No.08/027,628, filed Mar. 10, 1993, now abandoned, which is acontinuation-in-part of International Patent Application No.PCT/US92/04438 filed Jun. 3, 1992, which designated the U.S.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to lubricant base stocks, which can also serve ascomplete lubricants in some cases; compounded lubricants, which includeat least one additive for such purposes as improving high pressureresistance, corrosion inhibition, and the like along with the lubricantbase stocks which contribute the primary lubricity to the compoundedlubricants; refrigerant working fluids including lubricants according tothe invention along with primary heat transfer fluids, and methods forusing these materials. The lubricants and lubricant base stocks aregenerally suitable for use with most or all halocarbon refrigerants andare particularly suitable for use with substantially chlorine-free,fluoro-group-containing organic refrigerating heat transfer fluids suchas pentafluoroethane, 1,1-difluoroethane, 1,1,1-trifluroethane, andtetrafluoroethanes, most particularly 1,1,1,2-tetrafluoroethane. Thelubricants and base stocks, in combination with these heat transferfluids, are particularly suitable for hermetically sealed compressorsfor domestic air conditioners and refrigerators, where long lubricantservice lifetimes are important because of the difficulty and expense ofsupplying additional lubricant after the initial assembly of thecompressor.

2. Statement of Related Art

Chlorine-free heat transfer fluids are desirable for use in refrigerantsystems, because their escape into the atmosphere causes less damage tothe environment than the currently most commonly used chlorofluorocarbonheat transfer fluids such as trichlorofluoromethane anddichlorodifluoromethane. The widespread commercial use of chlorine-freerefrigerant heat transfer fluids has been hindered, however, by the lackof commercially adequate lubricants. This is particularly true for oneof the most desirable working fluids, 1,1,1,2-tetrafluoroethane,commonly known in the art as “Refrigerant 134a” or simply “R134a”. Otherfluoro-substituted ethanes are also desirable working fluids.

Esters of hindered polyols, which are defined for this purpose asorganic molecules containing at least five carbon atoms, at least 2-OHgroups, and no hydrogen atoms on any carbon atom directly attached to acarbon atom bearing an —OH group, have already been recognized in theart as high quality lubricant basestocks for almost any type ofrefrigeration machinery employing a fluorocarbon refrigerant,particularly one free from chlorine. The following patents and publishedpatent applications also teach many general classes and specificexamples of polyol esters useful as refrigerant lubricants withchlorine-free fluoro group containing heat transfer fluids: U.S. Pat.No. 4,851,144; UK 2 216 541; U.S. Pat. Nos. 5,021,179; 5,096,606; WO90/12849 (Lubrizol); EP 0 406 479 (Kyodo Oil); EP 0 430 657 (Asahi DenkaKK); EP 0 435 253 (Nippon Oil); EP 0 445 610 and 0 445 611 (Hoechst AG);EP 0449 406; EP 0 458 584 (Unichema Chemie BV); and EP 0 485 979(Hitachi).

DESCRIPTION OF THE INVENTION

Except in the claims and the operating examples, or where otherwiseexpressly indicated, all numerical quantities in this descriptionindicating amounts of material or conditions of reaction and/or use areto be understood as modified by the term “about” in defining thebroadest scope of the invention. Practice of the invention within theboundaries corresponding to the exact quantities stated is usuallypreferable, however.

More specifically, esters according to this invention should have aviscosity of not more than 44, or with increasing preference in theorder given, not more than 42, 40, 38.5, 37.2, 36.6, 36.2, 35.7, or35.2, centistokes at 40° C. Independently, esters according to thisinvention should have a viscosity of at least 22.5, or with increasingpreference in the order given, at least 23.9, 25.0, 25.9, 26.7, 27.4,28.0, 28.5, 29.0, 29.4, or 29.8, centistokes at 40° C.

It has now been found that selected polyol esters provide high qualitylubrication for this kind of service. Specifically effective are estersor mixtures of esters made by reacting (i) a mixture of alcoholmolecules selected from the group consisting of 2,2-dimethylol-1-butanol(also known as “trimethylolpropane” and often abbreviated hereinafter as“TMP”); di-trimethylolpropane (often abbreviated hereinafter as “DTMP”),a molecule with four hydroxyl groups and one ether linkage, formallyderived from two molecules of TMP by removing one hydroxyl group fromone of the TMP molecules and one hydrogen atom from a hydroxyl group ofthe other TMP molecule to form water and join the two remainders of theoriginal TMP molecules with an ether bond;2,2-dimethylol-1,3-propanediol (also known as “pentaerythritol” andoften abbreviated hereinafter as “PE”); and di-pentaerythritol (oftenabbreviated hereinafter as “DPE”), a molecule with six hydroxyl groupsand one ether bond, formally derived from two PE molecules by the sameelimination of the elements of water as described above for DTMP, with(ii) a mixture of acid molecules selected from the group consisting ofall the straight and branched chain monobasic and dibasic carboxylicacids with from four to twelve carbon atoms each, with the alcoholmoieties and acyl groups in the mixture of esters selected subject tothe constraints that (a) a total of at least 3%, or, with increasingpreference in the order given, at least 7, 10, 14, 16, or 19%, of theacyl groups in the mixture 2-methylbutanoyl or 3-methylbutanoyl groups,which are jointly abbreviated hereinafter as “acyl groups from i-C₅acid”; (b) the ratio of the % of acyl groups in the mixture that contain8 or more carbon atoms and are unbranched to the % of acyl groups in themixture that are both branched and contain not more than six, preferablynot more than five, carbon atoms is not greater than 1.56, morepreferably not greater than 1.21, or still more preferably not greaterthan 1.00; (c) the % of acyl groups in the ester mixture that contain atleast nine carbon atoms, whether branched or not, is not greater than81, or increasingly more preferably, not greater than 67 or 49; and (d)not more than 2, more preferably not more than 1, or still morepreferably not more than 0.4, % of the acyl groups in the ester mixtureare from acid molecules with more than two carboxyl groups each; andeither (d)(1) a total of at least 20, or, with increasing preference inthe order given, at least 29, 35, or 41% of the acyl groups in themixture are from one of the trimethylhexanoic acids, most preferablyfrom 3,5,5-trimethylhexanoic acid; and not more than 7.5, or, withincreasing preference in the order given, not more than 6.0, 4.5, 3.0,1.7, 0.9, or 0.4% of the acyl groups in the acid mixture are fromdibasic acids; or (d)(2) at least 2.0, or with increasing preference inthe order given, at least 2.8, 3.6, 4.1, or 4.9, %, but not more than13%, preferably not more than 10%, or still more preferably not morethan 7.0%, of the acyl groups in the ester mixture are from dibasic acidmolecules; and a total of at least 82, or with increasing preference inthe order given, at least 85, 89, 93, 96, or 99% of the monobasic acylgroups in the acid mixture have either five or six, or more preferablyexactly five, carbon atoms each. In all these percentages, acyl groupsare counted as a single group, irrespective of the number of valencesthey have. For example, each molecule of adipic acid yields a single,dibasic, acyl group when completely esterified.

(Of course, for all the types of esters described herein as part of theinvention, it is possible to obtain the same esters or mixture of estersby reacting acid derivatives such as acid anhydrides, acyl chlorides,and esters of the acids with lower molecular weight alcohols than thosedesired in the ester products according to this invention, instead ofreacting the acids themselves. The acids are generally preferred foreconomy and are normally specified herein, but it is to be understoodthat the esters defined herein by reaction with acids can be equallywell obtained by reaction of alcohols with the corresponding acidderivatives, or even by other reactions. The only, critical feature isthe mixture of acyl groups and alcohol moieties in the final mixture ofesters formed.)

Preferably, with increasing preference in the order given, at least 60,75, 85, 90, 95, or 98% of the hydroxyl groups in the mixture of alcoholsreacted to make esters according to this invention are moieties of PEmolecules. Independently, in the mixtures reacted to make the estersaccording to this invention, with increasing preference in the ordergiven, at least 60, 75, 85, 90, 95, or 98% of the monobasic acidmolecules in the acid mixture consist of molecules having no more thanten carbon atoms each and, with increasing preference in the ordergiven, at least 60, 75, 85, 90, 95, or 98% of the dibasic acid moleculesin the acid mixture consist of molecules having no more than ten carbonatoms each, or more preferably from five to seven carbon atoms each.Most preferably, with increasing preference in the order given, at least60, 75, 85, 90, 95, or 98% of the monobasic acid molecules in the acidmixture consist of molecules having either five or nine carbon atomseach.

These preferences for the acyl groups and alcohol moieties in estersaccording to this invention are based on empirically determinedgeneralizations. In order to achieve the desired middle range ofviscosity, corresponding approximately to ISO grades 22-46, it isadvantageous to have a substantial fraction of alcohols with at leastfour hydroxyl groups. Among the commercially available hindered alcoholsthat satisfy this criterion, PE is less expensive than DTMP and is freefrom the ether linkage in DTMP, which increases the hygroscopicity ofthe esters formed and thereby may promote undesirable corrosion of themetal surfaces lubricated. Alcohols with more than four hydroxyl groupsproduce esters with higher than optimum viscosities, but some suchesters can be tolerated, and mixtures including them may be cheaper.Commercial grade PE often contains a substantial amount of DPE, andcosts at least a little less than more purified PE. When cost factorsare not severely constraining, removing most or all of the DPE from apredominantly PE mixture of alcohols used to make the esters ispreferable, in order to minimize the chance of insolubility of part ofthe ester mixture at low temperatures.

In order to obtain esters with adequate viscosity, a considerablefraction of the acid molecules reacted need to have eight or more carbonatoms or be dibasic. Dibasic acids are less desirable. They must beused, if at all, in rather small amounts in order to avoid excessiveviscosity, because of the capability of forming very high molecularweight and very viscous oligomers or polymers by reaction betweenalcohol and acid molecules that both have at least two functionalgroups. In practice, it has been found that the amount of dibasic acidthat can be effectively used in the acid mixture reacted to make estersaccording to this invention is substantially less than the amount thatwould be sufficient to provide at least one dibasic acid group to linkeach two alcohol molecules in the alcohol mixture also reacted.Therefore, when such amounts of dibasic acid are used, some of thealcohol molecules will be joined together in the esters formed and somewill not; the esters with two or more alcohol moieties will be much moreviscous and normally less readily soluble in the fluorocarbonrefrigerant fluids than the other esters in the mixture, those with onlyone alcohol moiety, thereby increasing the risk of undesirable phaseseparation in the course of use of the esters. However, limited amountsof dibasic acid may nevertheless be used, as already noted above.

When substantially only monobasic acids are used to make the esters, asalready noted, in order to obtain adequate viscosity in the mixture, asubstantial fraction of the acid molecules must have at least eightcarbon atoms. With acids of such length, solubility in the fluorocarbonrefrigerant fluids is less than for esters with shorter acids, and thisreduced solubility is particularly marked for straight chain acids, sothat a substantial fraction of the longer acids normally needs to bebranched; alternatively, it has been found that these longer straightchain acids can be “balanced” for solubility with an equal or not toomuch less than equal fraction of branched acids with five or six carbonatoms. When the number of carbon atoms per molecule is nine or more, noteven branching is sufficient to produce adequate solubility by itself,so that an upper limit on the fraction of such acids is independentlyrequired. In general, a minimum amount of the particularly advantageousi-C₅ acid is specified to aid in solubilizing the parts of the esters inthe mixture that contain dibasic acids or those with eight or morecarbon atoms.

For both performance and economic reasons, it has been found that fiveand nine carbon monobasic acids are the most preferred constituents, andthey are very effective in balancing each other to achieve a mix ofviscosity and solubility characteristics that is better suited thanothers to most applications. Trimethylhexanoic acids, with their threemethyl branches, produce the most soluble esters among the readilyavailable nine carbon acids. (In general, methyl branches are the mosteffective in promoting solubility without increasing viscosityexcessively, because of the larger number of carbon atoms in otherbranching groups.) Branches on the carbon alpha to the carboxyl increasethe difficulty of esterification and do not appear to be any moreeffective in increasing solubility than more remotely located branches.The most economical commercially available mixture of branched ninecarbon acids, which contains from 88-95 mole % of3,5,5-trimethylhexanoic acid with all but at most 1 mole % of theremainder being other branched C₉ monobasic acids, appears at least aseffective as any other and is therefore preferred for economic reasonsas the source of C₉ monobasic acids.

It is to be understood that only the desired alcohols and acids areexplicitly specified, but some amount of the sort of impurities normallypresent in commercial or industrial grade products can be tolerated inmost cases. For example, commercial pentaerythritol normally containsonly about 85-90 mole % of pure pentaerythritol, along with 10-15 mole tof di-pentaerythritol, and commercial pentaerythritol is satisfactoryfor use in making lubricant esters according to this invention in manycases. In general, however, it is preferred, with increasing preferencein the order given, that not more than 25, 21, 17, 12, 8, 5, 3, 2, 1,0.5, or 0.2% of either the hydroxyl groups in the alcohol mixturesspecified herein or of the carboxyl groups in the acid mixturesspecified herein should be part of any molecules other than thoseexplicitly specified for each type of lubricant base stock. Percentagesof specific chemical molecules or moieties specified herein, such as thepercentages of carboxyl and hydroxyl groups stated in the precedingsentence, are to be understood as number percentages, which will bemathematically identical to percentages by chemical equivalents, withAvogadro's number of each specified chemical moiety regarded as a singlechemical equivalent.

The above descriptions for each of the acid and alcohol mixtures reactedto produce lubricant esters according to this invention refers only tothe mixture of acids or alcohols that actually reacts to form esters anddoes not necessarily imply that the mixtures of acids or alcoholscontacted with each other for the purpose of reaction will have the samecomposition as the mixture that actually reacts. In fact, it has beenfound that reaction between the alcohol(s) and the acid(s) used proceedsmore effectively if the quantity of acid charged to the reaction mixtureinitially is enough to provide an excess of 10-25% of equivalents ofacid over the equivalents of alcohol reacted with the acid. (Anequivalent of acid is defined for the purposes of this specification asthe amount containing one gram equivalent weight of carboxyl groups,while an equivalent of alcohol is the amount containing one gramequivalent weight of hydroxyl groups.) The composition of the mixture ofacids that actually reacted can be determined by analysis of the productester mixture for its acyl group content.

In making most or all of the esters and mixtures of esters preferredaccording to this invention, the acid(s) reacted will be lower boilingthan the alcohol(s) reacted and the product ester(s). When thiscondition obtains, it is preferred to remove the bulk of any excess acidremaining at the end of the esterification reaction by distillation,most preferably at a low pressure such as 1-5 torr.

After such vacuum distillation, the product is often ready for use as alubricant or lubricant base stock according to this invention. Iffurther refinement of the product is desired, the content of free acidin the product after the first vacuum distillation may be furtherreduced by treatment with epoxy esters as taught in U.S. Pat. No.3,485,754 or by neutralization with any suitable alkaline material suchas lime, alkali metal hydroxide, or alkali metal carbonates. Iftreatment with epoxy esters is used, excess epoxy ester may be removedby a second distillation under very low pressure, while the products ofreaction between the epoxy ester and residual acid may be left behind inthe product without harm. If neutralization with alkali is used as therefinement method, subsequent washing with water, to remove anyunreacted excess alkali and the small amount of soap formed from theexcess fatty acid neutralized by the alkali, is strongly preferredbefore using the product as a lubricant and/or base stock according tothis invention.

Under some conditions of use, the ester(s) as described herein willfunction satisfactorily as complete lubricants. It is generallypreferable, however, for a complete lubricant to contain other materialsgenerally denoted in the art as additives, such as oxidation resistanceand thermal stability improvers, corrosion inhibitors, metaldeactivators, lubricity additives, viscosity index improvers, pourand/or floc point depressants, detergents, dispersants, antifoamingagents, anti-wear agents, and extreme pressure resistant additives. Manyadditives are multifunctional. For example, certain additives may impartboth anti-wear and extreme pressure resistance properties, or functionboth as a metal deactivator and a corrosion inhibitor. Cumulatively, alladditives preferably do not exceed 8% by weight, or more preferably donot exceed 5% by weight, of the total compounded lubricant formulation.

An effective amount of the foregoing additive types is generally in therange from 0.01 to 5% for the anti-oxidant component, 0.01 to 5% for thecorrosion inhibitor component, from 0.001 to 0.5% for the metaldeactivator component, from 0.5 to 5% for the lubricity additives, from0.01 to 2% for each of the viscosity index improvers and pour and/orfloc point depressants, from 0.1 to 5% for each of the detergents anddispersants, from 0.001 to 0.1% for anti-foam agents, and from 0.1-2%for each of the anti-wear and extreme pressure resistance components.All these percentages are by weight and are based on the total lubricantcomposition. It is to be understood that more or less than the statedamounts of additives may be more suitable to particular circumstances,and that a single molecular type or a mixture of types may be used foreach type of additive component. Also, the examples listed below areintended to be merely illustrative and not limiting, except as describedin the appended claims.

Examples of suitable oxidation resistance and thermal stabilityimprovers are diphenyl-, dinaphthyl-, and phenylnaphthyl-amines, inwhich the phenyl and naphthyl groups can be substituted, e.g.,N,N′-diphenyl phenylenediamine, p-octyldiphenylamine,p,p-dioctyldiphenylamine, N-phenyl-1-naphthyl amine, N-phenyl-2-naphthylamine, N-(p-dodecyl)phenyl-2-naphthyl amine, di-1-naphthylamine, anddi-2-naphthylamine; phenothazines such as N-alkylphenothiazines;imino(bisbenzyl); and hindered phenols such as 6-(t-butyl) phenol,2,6-di-(t-butyl) phenol, 4-methyl-2,6-di-(t-butyl) phenol,4,4′-methylenebis(-2,6-di-{t-butyl}phenol), and the like.

Examples of suitable cuprous metal deactivators are imidazole,benzamidazole, 2-mercaptobenzthiazole, 2,5-di-mercaptothiadiazole,salicylidine-propylenediamine, pyrazole, benzotriazole, tolutriazole,2-methylbenzamidazole, 3,5-dimethyl pyrazole, and methylenebis-benzotriazole. Benzotriazole derivatives are preferred. Otherexamples of more general metal deactivators and/or corrosion inhibitorsinclude organic acids and their esters, metal salts, and anhydrides,e.g., N-oleyl-sarcosine, sorbitan monooleate, lead naphthenate,dodecenyl-succinic acid and its partial esters and amides, and4-nonylphenoxy acetic acid; primary, secondary, and tertiary aliphaticand cycloaliphatic amines and amine salts of organic and inorganicacids, e.g., oil-soluble alkylammonium carboxylates; heterocyclicnitrogen containing compounds, e.g., thiadiazoles, substitutedimidazolines, and oxazolines; quinolines, quinones, and anthraquinones;propyl gallate; barium dinonyl naphthalene sulfonate; ester and amidederivatives of alkenyl succinic anhydrides or acids, dithiocarbamates,dithiophosphates; amine salts of alkyl acid phosphates and theirderivatives.

Examples of suitable lubricity additives include long chain derivativesof fatty acids and natural oils, such as esters, amines, amides,imidazolines, and borates.

Examples of suitable viscosity index improvers includepolymethacrylates, copolymers of vinyl pyrrolidone and methacrylates,polybutenes, and styrene-acrylate copolymers.

Examples of suitable pour point and/or floc point depressants includepolymethacrylates such as methacrylateethylene-vinyl acetateterpolymers; alkylated naphthalene derivatives; and products ofFriedel-Crafts catalyzed condensation of urea with naphthalene orphenols.

Examples of suitable detergents and/or dispersants includepolybutenylsuccinic acid amides; polybutenyl phosphonic acidderivatives; long chain alkyl substituted aromatic sulfonic acids andtheir salts; and metal salts of alkyl sulfides, of alkyl phenols, and ofcondensation products of alkyl phenols and aldehydes.

Examples of suitable anti-foam agents include silicone polymers and someacrylates.

Examples of suitable anti-wear and extreme pressure resistance agentsinclude sulfurized fatty acids and fatty acid esters, such as sulfurizedoctyl tallate; sulfurized terpenes; sulfurized olefins;organopolysulfides; organo phosphorus derivatives including aminephosphates, alkyl acid phosphates, dialkyl phosphates,aminedithiophosphates, trialkyl and triaryl phosphorothionates, trialkyland triaryl phosphines, and dialkylphosphites, e.g., amine salts ofphosphoric acid monohexyl ester, amine salts of dinonylnaphthalenesulfonate, triphenyl phosphate, trinaphthyl phosphate, diphenyl cresyland dicresyl phenyl phosphates, naphthyl diphenyl phosphate,triphenylphosphorothionate; dithiocarbamates, such as an antimonydialkyl dithiocarbamate; chlorinated and/or fluorinated hydrocarbons,and xanthates.

Under some conditions of operation, it is believed that the presence inlubricants of the types of polyether polyols that have been prominentconstituents of most prior art lubricant base stocks taught as usefulwith fluorocarbon refrigerant working fluids are less than optimallystable and/or inadequately compatible with some of the most usefullubricant additives. Thus, in one embodiment of this invention, it ispreferred that the lubricant base stocks and lubricants be substantiallyfree of such polyether polyols. By “substantially free”, it is meantthat the compositions contain no more than about 10% by weight,preferably no more than about 2.6% by weight, and more preferably nomore than about 1.2% by weight of the materials noted.

One major embodiment of the present invention is a refrigerant workingfluid comprising both a suitable heat transfer fluid such as afluorocarbon and a lubricant according to this invention. Preferably,the refrigerant working fluid and the lubricant should have chemicalcharacteristics and be present in such a proportion to each other thatthe working fluid remains homogeneous, i.e., free from visuallydetectable phase separations or turbidity, over the entire range ofworking temperatures to which the working fluid is exposed duringoperation of a refrigeration system in which the working fluid is used.This working range may vary from −60° C. to as much as +175° C. It isoften adequate if the working fluid remains single phase up to +30° C.,although it is increasingly more preferable if the single phase behavioris maintained up to 40, 56, 71, 88, or 100° C. Similarly, it is oftenadequate if the working fluid compositions remains a single phase whenchilled to 0° C., although it is increasingly more preferable if thesingle phase behavior persists to −10, −20, −30, −40, or −55° C. Singlephase mixtures with chlorine free hydrofluorocarbon refrigerant workingfluids are usually obtained with the suitable and preferred types ofesters described above.

Inasmuch as it is often difficult to predict exactly how much lubricantwill be mixed with the heat transfer fluid to form a working fluid, itis most preferable if the lubricant composition forms a single phase inall proportions with the heat transfer fluid over the temperature rangesnoted above. This however, is a very stringent requirement, and it isoften sufficient if there is single phase behavior over the entiretemperature range for a working fluid mixture containing up to 1% byweight of lubricant according to this invention. Single phase behaviorover a temperature range for mixtures containing up to 2, 4, 10, and 15%by weight of lubricant is successively more preferable.

In some cases, single phase behavior is not required. The term“miscible” is used in the refrigeration lubrication art and hereinafter,except when part of the phrase “miscible in all proportions”, when twophases are formed but are readily capable of being mixed into a uniformdispersion that remains stable as long as it is at least moderatelyagitated mechanically. Some refrigeration (and other) compressors aredesigned to operate satisfactorily with such miscible mixtures ofrefrigerant working fluid and lubricant. In contrast, mixtures that leadto coagulation or significant thickening and form two or more phases areunacceptable commercially and are designated herein as “immiscible”. Anysuch mixture described below is a comparative example and not anembodiment of the present invention.

Another major embodiment of the invention is the use of a lubricantaccording to the invention, either as total lubricant or lubricant basestock, in a process of operating refrigerating machinery in such amanner that the lubricant is in contact with the refrigerant workingfluid.

The practice of the invention may be further understood and appreciatedby consideration of the following examples and comparative examples.

General Ester Synthesis Procedure

The alcohol(s) and acid(s) to be reacted, together with a suitablecatalyst such as dibutyltin diacetate, tin oxalate, phosphoric acid,and/or tetrabutyl titanate, were charged into a round bottomed flaskequipped with a stirrer, thermometer, nitrogen sparging means,condenser, and a recycle trap. Acid(s) were charged in about a 15% molarexcess over the alcohol(s). The amount of catalyst was from 0.02 to 0.1%by weight of the weight of the total acid(s) and alcohol(s) reacted.

The reaction mixture was heated to a temperature between about 220 and230° C., and water from the resulting reaction was collected in the trapwhile refluxing acids were returned to the reaction mixture. Partialvacuum was maintained above the reaction mixture as necessary to achievea reflux rate of between 8 and 12% of the original reaction mixturevolume per hour.

The reaction mixture was sampled occasionally for determination ofhydroxyl number, and after the hydroxyl number had fallen below 5.0 mgof KOH per gram of mixture, the majority of the excess acid was removedby distillation after applying the highest vacuum obtainable with theapparatus used, corresponding to a residual pressure of about 0.05 torr,while maintaining the reaction temperature. The reaction mixture wasthen cooled, and any residual acidity was removed, if desired, bytreatment with lime, sodium hydroxide, or epoxy esters. The resultinglubricant or lubricant base stock was dried and filtered before phasecompatibility testing.

General Procedure for Phase Compatibility Testing

One milliliter (“ml”) of the lubricant to be tested is placed into athermal shock resistant, volumetrically graduated glass test tube 17millimeters (“mm”) in diameter and 145 mm long. The test tube is thenstoppered and placed into a cooling bath regulated to −29±0.2° C. Afterthe tube and contents have equilibrated in the cooling bath for 5minutes (“min”), sufficient refrigerant working fluid is added to give atotal volume of 10 ml.

At least 15 min after the working fluid has been added, during whichtime the tube and contents have been equilibrating in the cooling bathand the contents may have been agitated if desired, the tube contentsare visually examined for evidence of phase separation. If there is anysuch phase separation, the tube is shaken to determine whether thecombination can be rated as miscible or is totally unacceptable.

If there is no evidence of phase separation at −29° C., the temperatureof the cooling bath is usually lowered at a rate of 0.3° per min untilphase separation is observed. The temperature of first observation ofphase separation, if within the range of the cooling equipment used, isthen noted as the insolubility onset temperature.

Composition of Specific Examples

A suitable ester mixture as described above was prepared by reacting amixture of alcohol molecules in which 99.4% were PE molecules, with mostof the remainder being DPE molecules, with a mixture of acid moleculesthat included 46.7% of pentanoic (=n-valeric) acid, 21.5% of2-methylbutanoic acid, and 31.6% of 3,5,5-trimethylhexanoic acid, withthe remainder predominantly other branched C₉ monobasic acids. Thisester mixture had an ISO grade of 32.

A second suitable ester mixture as described above was prepared byreacting a mixture of alcohol molecules in which 99.4% were PEmolecules, with most of the remainder being DPE molecules, with amixture of acid molecules that included 66.8% of pentanoic (=n-valeric)acid, 28.4% of 2-methylbutanoic acid, and 4.6% of adipic acid, with theremainder being predominantly 3-methylbutanoic acid. This lubricant basestock had an ISO grade of 32.

The invention claimed is:
 1. A refrigerant working fluid consistingessentially of a heat transfer fluid consisting of a substantiallychlorine-free fluoro-group containing organic refrigerating heattransfer fluid and a composition of matter suitable for serving as alubricant or lubricant base stock, said composition being a liquid witha viscosity between about 22.5 and about 44 centistokes at 40° C.,remaining in a single phase with the heat transfer fluid between about−40° C. and about +71° C. and consisting essentially of a mixture ofpolyol ester molecules in which at least about 92% of the alcoholmoieties are selected from the group consisting of the alcohol moietiesderived from TMP, DTMP, PE and DPE and in which only monobasic acids areused to make the ester, said monobasic acid groups being furtherselected subject to the constraints that (a) the % of monobasic acidgroups in the mixture that contain at least nine carbon atoms whetherbranched or not is not greater than about 67; (b) a total of at leastabout 20% of the monobasic acid groups in the mixture are from one ofthe trimethylhexanoic acids and (c) at least about 60% carbon atoms ofthe monobasic acid groups in the acid mixture consist of moleculeshaving either five or nine carbon atoms each.
 2. A refrigerant workingfluid consisting essentially of a heat transfer fluid consisting of asubstantially chlorine-free fluoro-group containing organicrefrigerating heat transfer fluid and a composition of matter suitablefor serving as a lubricant or lubricant base stock, said compositionbeing a liquid with a viscosity between about 22.5 and about 44centistokes at 40° C., remaining in a single phase with the heattransfer fluid between about −40° C. and about +71° C. and consistingessentially of a mixture of polyol ester molecules in which at leastabout 92% of the alcohol moieties are selected from the group consistingof the alcohol moieties derived from TMP, DTMP, PE and DPE, at leastabout 60% of the hydroxyl groups in the mixture of alcohol moieties aremoieties of PE molecules and in which only monobasic acids are used tomake the ester, said monobasic acid groups being further selectedsubject to the constraints that (a) the % of monobasic acid groups inthe mixture that contain at least nine carbon atoms whether branched ornot is not greater than about 67; (b) a total of at least about 20% ofthe monobasic acid groups in the mixture are from one of thetrimethylhexanoic acids and (c) at least about 60% of the monobasic acidgroups in the acid mixture consist of molecules having either five ornine carbon atoms each.
 3. The refrigerant working fluid according toclaim 2 consisting essentially of a heat transfer fluid consisting of asubstantially chlorine-free fluoro-group containing organicrefrigerating heat transfer fluid and a composition of matter suitablefor serving as a lubricant or lubricant base stock, said compositionbeing a liquid with a viscosity between about 22.5 and about 44centistokes at 40° C., and remaining in a single phase with the heattransfer fluid between about −40° C. and about +71° C. and consistingessentially of a mixture of polyol ester molecules in which at leastabout 92% of the alcohol moieties are selected from the group consistingof the alcohol moieties derived from TMP, DTMP, PE and DPE, at leastabout 85% of the hydroxyl groups in the mixture of alcohol moieties aremoieties of PE molecules and in which only monobasic acids are used tomake the ester, said monobasic acid groups being further selectedsubject to the constraints that (a) the % of monobasic acid groups inthe mixture that contain at least nine carbon atoms whether branched ornot is not greater than about 67; (b) a total of at least about 20% ofthe monobasic acid groups in the mixture are from one of thetrimethylhexanoic acids and (c) at least about 60% of the monobasic acidgroups in the acid mixture consist of molecules having either five ornine carbon atoms each.
 4. The refrigerant working fluid according toclaim 2 consisting essentially of a heat transfer fluid consisting of asubstantially chlorine-free fluoro-group containing organicrefrigerating heat transfer fluid and a composition of matter suitablefor serving as a lubricant or lubricant base stock, said compositionbeing a liquid with a viscosity between about 22.5 and about 44centistokes at 40° C., remaining in a single phase with the heattransfer fluid between about −55° C. and about +71° C. and consistingessentially of a mixture of polyol ester molecules in which at leastabout 92% of the alcohol moieties are selected from the group consistingof the alcohol moieties derived from TMP, DTMP, PE and DPE, at leastabout 85% of the hydroxyl groups in the mixture of alcohol moieties aremoieties of PE molecules and in which only monobasic acids are used tomake the ester, said acyl groups being further selected subject to theconstraints that (a) the % of the monobasic acid groups in the mixturethat contain at least nine carbon atoms whether branched or not is notgreater than about 67; (b) a total of at least about 29% of themonobasic acid groups in the mixture are from one of thetrimethylhexanoic acids and (c) at least about 90% of the monobasic acidgroups in the acid mixture consist of molecules having either five ornine carbon atoms each.
 5. The refrigerant working fluid according toclaim 2 consisting essentially of a heat transfer fluid consisting of asubstantially chlorine-free fluoro-group containing organicrefrigerating heat transfer fluid and a composition of matter suitablefor serving as a lubricant or lubricant base stock, said compositionbeing a liquid with a viscosity between about 26.7 and about 40centistokes at 40° C., remaining in a single phase with the heattransfer fluid between about −55° C. and about +71° C. and consistingessentially of a mixture of polyol ester molecules in which at leastabout 92% of the alcohol moieties are selected from the group consistingof the alcohol moieties derived from TMP, DTMP, PE and DPE, at leastabout 85% of the hydroxyl groups in the mixture of alcohol moieties aremoieties of PE molecules and in which only monobasic acids are used tomake the ester, said acyl groups being further selected subject to theconstraints that (a) the % of monobasic acid groups in the mixture thatcontain at least nine carbon atoms whether branched or not is notgreater than about 67; (b) a total of at least about 29% of themonobasic acid groups in the mixture are from one of thetrimethylhexanoic acids and (c) at least about 95% of the monobasic acidgroups in the acid mixture consist of molecules having either five ornine carbon atoms each.
 6. The refrigerant working fluid according toclaim 2 consisting essentially of a heat transfer fluid consisting of asubstantially chlorine-free fluoro-group containing organicrefrigerating heat transfer fluid and a composition of matter suitablefor serving as a lubricant or lubricant base stock, said compositionbeing a liquid with a viscosity between about 28.5 and about 35.2centistokes at 40° C., remaining in a single phase with the heattransfer fluid between about −55° C. and about +71° C. and consistingessentially of a mixture of polyol ester molecules in which at leastabout 92% of the alcohol moieties are selected from the group consistingof the alcohol moieties derived from TMP, DTMP, PE and DPE, at leastabout 85% of the hydroxyl groups in the mixture of alcohol moieties aremoieties of PE molecules and in which only monobasic acids are used tomake the ester, said monobasic acid groups being further selectedsubject to the constraints that (a) the % of the monobasic acid groupsin the mixture that contain at least nine carbon atoms whether branchedor not is not greater than about 49; (b) a total of at least about 29%of the monobasic acid groups in the mixture are from one of thetrimethylhexanol acids and (c) at least about 98% of the acyl groups inthe acid mixture consist of molecules having either five or nine carbonatoms each.
 7. The refrigerant working fluid consisting essentially of aheat transfer fluid consisting of a substantially chlorine-freefluoro-group containing organic refrigerating heat transfer fluid and acomposition of matter suitable for serving as a lubricant or lubricantbase stock, said composition being a liquid with a viscosity betweenabout 22.5 and about 44 centistokes at 40° C., remaining in a singlephase with the heat transfer fluid between about −40° C. and about +71°C. and consisting essentially of A) at least about 92% by weight of amixture of polyol ester molecules in which at least about 92% of thealcohol moieties are selected from the group consisting of the alcoholmoieties derived from TMP, DTMP, PE and DPE and in which only monobasicacids are used to make the ester, said monobasic acid groups beingfurther selected subject to the constraints that (a) the % of themonobasic acid groups in the mixture that contain at least nine carbonatoms whether branched or not is not greater than about 67; (b) a totalof at least about 20% of the monobasic acid groups in the mixture arefrom one of the trimethylhexanoic acids and (c) at least about 60% ofthe monobasic acid groups in the acid mixture consist of moleculeshaving either five or nine carbon atoms each and B) up to about 8% byweight of one or more additives selected from the group consisting ofoxidation resistance and thermal stability improvers, corrosioninhibitors, metal deactivators, lubricity additives, viscosity indeximprovers, pour and floc point depressants, detergents, dispersants,antifoaming agents, anti-wear agents and extreme pressure resistantadditives.
 8. The refrigerant working fluid according to claim 7consisting essentially of a heat transfer fluid consisting of asubstantially chlorine-free fluoro-group containing organicrefrigerating heat transfer fluid and a composition of matter suitablefor serving as a lubricant or lubricant base stock, said compositionbeing a liquid with a viscosity between about 22.5 and about 44centistokes at 40° C., and remaining in a single phase with the heattransfer fluid between about −40° C. and about +71° C. and consistingessentially of A) at least about 92% by weight of a mixture of polyolester molecules in which at least about 92% of the alcohol moieties areselected from the group consisting of the alcohol moieties derived fromTMP, DTMP, PE and DPE, at least about 85% of the hydroxyl groups in themixture of alcohol moieties are moieties of PE molecules and in whichonly monobasic acids are used to make the ester, said monobasic acidgroups being further selected subject to the constraints that (a) the %of the monobasic acid groups in the mixture that contain at least ninecarbon atoms whether branched or not is not greater than about 67; (b) atotal of at least about 20% of the monobasic acid groups in the mixtureare from one of the trimethylhexanol acids and (c) at least about 90% ofthe monobasic acid groups in the acid mixture consist of moleculeshaving either five or nine carbon atoms each and B) up to about 8% byweight of one or more additives selected from the group consisting ofoxidation resistance and thermal stability improvers, corrosioninhibitors, metal deactivators, lubricity additives, viscosity indeximprovers, pour and floc point depressants, detergents, dispersants,antifoaming agents, anti-wear agents and extreme pressure resistantadditives.
 9. The refrigerant working fluid according to claim 7consisting essentially of a heat transfer fluid consisting of asubstantially chlorine-free fluoro-group containing organicrefrigerating heat transfer fluid and a composition of matter suitablefor serving as a lubricant or lubricant base stock, said compositionbeing a liquid with a viscosity between about 22.5 and about 44centistokes at 40° C., remaining in a single phase with the heattransfer fluid between about −55° C. and about +71° C. and consistingessentially of A) at least about 92% by weight of a mixture of polyolester molecules in which at least about 92% of the alcohol moieties areselected from the group consisting of the alcohol moieties derived fromTMP, DTMP, PE and DPE, at least about 85% of the hydroxyl groups in themixture of alcohol moieties are moieties of PE molecules and in whichonly monobasic acids are used to make the ester, said monobasic acidgroups being further selected subject to the constraints that (a) the %of the monobasic acid groups in the mixture that contain at least ninecarbon atoms whether branched or not is not greater than about 67; (b) atotal of at least about 29% of the monobasic acid groups in the mixtureare from one of the trimethylhexanoic acids and (c) at least about 95%of the monobasic acid groups in the acid mixture consist of moleculeshaving either five or nine carbon atoms each and B) up to about 8% byweight of one or more additives selected from the group consisting ofoxidation resistance and thermal stability improvers, corrosioninhibitors, metal deactivators, lubricity additives, viscosity indeximprovers, pour and floc point depressants, detergents, dispersants,antifoaming agents, anti-wear agents and extreme pressure resistantadditives.
 10. The refrigerant working fluid according to claim 7consisting essentially of a heat transfer fluid consisting of asubstantially chlorine-free fluoro-group containing organicrefrigerating heat transfer fluid and a composition of matter suitablefor serving as a lubricant or lubricant base stock, said compositionbeing a liquid with a viscosity between about 26.7 and about 40centistokes at 40° C., remaining in a single phase with the heattransfer fluid between about −55° C. and about +71° C. and consistingessentially of A) at least about 92% by weight of a mixture of polyolester molecules in which at least about 92% of the alcohol moieties areselected from the group consisting of the alcohol moieties derived fromTMP, DTMP, PE and DPE, at least about 85% of the hydroxyl groups in themixture of alcohol moieties are moieties of PE molecules and in whichonly monobasic acids are used to make the ester, said monobasic acidgroups being further selected subject to the constraints that (a) the %of the monobasic acid groups in the mixture that contain at least ninecarbon atoms whether branched or not is not greater than about 67; (b) atotal of at least about 35% of the monobasic acid groups in the mixtureare from one of the trimethylhexanoic acids and (c) at least about 98%of the monobasic acid groups in the acid mixture consist of moleculeshaving either five or nine carbon atoms each and B) up to about 8% byweight of one or more additives selected from the group consisting ofoxidation resistance and thermal stability improvers, corrosioninhibitors, metal deactivators, lubricity additives, viscosity indeximprovers, pour and floc point depressants, detergents, dispersants,antifoaming agents, anti-wear agents and extreme pressure resistantadditives.
 11. The refrigerant working fluid according to claim 7consisting essentially of a heat transfer fluid consisting of asubstantially chlorine-free fluoro-group containing organicrefrigerating heat transfer fluid and a composition of matter suitablefor serving as a lubricant or lubricant base stock, said compositionbeing a liquid with a viscosity between about 28.5 and about 35.2centistokes at 40° C., remaining in a single phase with the heattransfer fluid between about −55° C. and about +71° C. and consistingessentially of A) at least about 92% by weight of a mixture of polyolester molecules in which at least about 92% of the alcohol moieties areselected from the group consisting of the alcohol moieties derived fromTMP, DTMP, PE and DPE, at least about 98% of the hydroxyl groups in themixture of alcohol moieties are moieties of PE molecules and in whichonly monobasic acids are used to make the ester, said monobasic acidgroups being further selected subject to the constraints (a) the % ofthe monobasic acid groups in the mixture that contain at least ninecarbon atoms whether branched or not is not greater than about 49; (b) atotal of at least about 41% of the monobasic acid groups in the mixtureare from one of the trimethylhexanol acids and (c) at least about 98% ofthe monobasic acid groups in the acid mixture consist of moleculeshaving either five or nine carbon atoms each and B) up to about 8% byweight of one or more additives selected from the group consisting ofoxidation resistance and thermal stability improvers, corrosioninhibitors, metal deactivators, lubricity additives, viscosity indeximprovers, pour and floc point depressants, detergents, dispersants,antifoaming agents, anti-wear agents and extreme pressure resistantadditives.
 12. The refrigerant working fluid according to claim 1wherein the chlorine-free fluoro-group containing organic refrigeratingheat transfer fluid comprises at least one of pentafluoroethane,1,1-difluoroethane, 1,1,1-trifluoroethane and tetrafluoroethane.
 13. Therefrigerant working fluid according to claim 12 wherein thechlorine-free fluoro-group containing organic refrigerating, heattransfer fluid is 1,1,1,2-tetrafluoroethane.
 14. The refrigerant workingfluid according to claim 2 wherein the chlorine-free fluoro-groupcontaining organic refrigerating heat transfer fluid comprises at leastone of pentafluoroethane, 1,1-difluoroethane, 1,1,1-trifluoroethane andtetrafluoroethane.
 15. The refrigerant working fluid according to claim3 wherein the chlorine-free fluoro-group containing organicrefrigerating heat transfer fluid comprises at least one ofpentafluoroethane, 1,1-difluoroethane, 1,1,1-trifluoroethane andtetrafluoroethane.
 16. The refrigerant working fluid according to claim4 wherein the chlorine-free fluoro-group containing organicrefrigerating heat transfer fluid comprises at least one ofpentafluoroethane, 1,1-difluoroethane, 1,1,1-trifluoroethane andtetrafluoroethane.
 17. The refrigerant working fluid according to claim7 wherein the chlorine-free fluoro-group containing organicrefrigerating heat transfer fluid comprises at least one ofpentafluoroethane, 1,1-difluoroethane, 1,1,1-trifluoroethane andtetrafluoroethane.
 18. The refrigerant working fluid according to claim17 wherein the chlorine-free fluoro-group containing organicrefrigerating heat transfer fluid is 1,1,1,2-tetrafluoroethane.
 19. Aprocess for operating a refrigerator comprising cyclic compression,liquefaction, expansion, and evaporation of the refrigerant workingfluid as claimed in claim
 1. 20. A process for operating a refrigeratorcomprising cyclic compression, liquefaction, expansion, and evaporationof the refrigerant working fluid as claimed in claim 7.